Well I've hooked and landed some big Chum Salmon with a 5wt on the Skagit River fishing for dollies. I see no problem with that size rod And my tippet size was about 8 lbs. If the fish is too big I just break it off. I just fish for fun. If I catch something or not I don't really care.

Durable and capable yet light enough to enjoy smaller sea run Cutthroats. One of my favorite summer rods is an old Bamboo 7wt by Bill Phillipson the one I like the most was owned first by a fellow in Conneticut and he bought it brand new in 1949. I was then one year old!

I agree with Moose, anything from 17# to 1# as long as it sells for enough money to get another 12'4" 8/9# Loop double hander.
Preferably a Greenline and the appropiate Loop adaptive head and tip. Or a few SA T40's.
All of which means there isn't a best 9 footer, its all myth, but there is a best double hander, which fits everything, fresh to salt.
Cherers Max

Ah but you guys were talking about the "most useful", and "light" and a 15' Talon is not the most useful, nor is it light. Since I don't fish for trout, introduced feral rubbish out here, I can't think of a place I'd use a light fly rod in 9 foot in salt water. No a light double hander in 12 foot is another matter entirely. I have 9 foters but I havent put a reel on one in a year. Max

I'm 85% flats sight fisherman and 15% big surf and rip currents here on Cape Cod's striped bass flats, so the single hander still has an important role in my arsenal... but lately I've been playing with super-light 10.5-11ft 9wt prototypes that cast just like throwing darts for accuracy in the sight fishing game on the flats while also making longer casts with easy effort when needed. They are so light (just over 7oz) that overhand casting with a double haul is easy as well.

It's redefining the way I sight fish on the flats. I will have them on some bonefish flats for some field testing prior to the striper season. Randall Kaufmann states in his book that bonefishing is mostly 30ft casts made for accuracy. I have to agree with that assessment. I've been really surprised at how an 11ft rod can throw laser beam casts with accuracy even across the body (to deal with wind) with eyes focused on the fish and no movement of the feet or legs to make the cast.

Two-handers as flats rods? I wouldn't have believed it myself until Nobuo sent me this last prototype!

Well I'm not a flats fly fisherman, but from the stuff I've done I think distance is relative to the height of the tip above the water, and a DH rod gives a longer cast, and that means greater coverage, if you are fishing for area. If you are wading flats looking for fish and casting to them the range is not that long, and you can roll cast DH rods in the 12' class very accurately, and quickly. From a position of knee deep in water, or deeper, your vision is not that long, and even polaroiding you aren't looking for fish 120 feet away, mostly its 50 feet or so.
If you want to go to excesses you might try a 14 footer, but I rather think a rod in the 12' class would be great stuff. I know my Loop is fabulous. Fact is it's a 8/9 weight and I detest the idea of 9 footers in that class. I have a 10' 9# TFO, but thats it.
If I fish the local estuary flats, I'm looking for flathead mostly and its all blind casting and coverage, ease of casting and fly retrieve speed can be critical. Added to this is the fact that you can choose to go out there and overhead cast or you can simply roll cast the thing. With roll casting you get rid of shooting line management which is a serious problem with 9 footers. In fact with DH outfits I think that a lot of the problems one has with 9 footers just do not occur.
If you fish out of boats, I think the same applies, even though you might be a bit higher off the water. In any case longer casts might be just what the doctor ordered.
I have chased a few tuna in my time and quite often a longer casting outfit will get you at skittish fish wheras a 9 footer is a bit of a bummer because of the time needed to get enough line velocity to get a longer cast.
I just think that the DH potential is virtually unplumbed, even by gurus, and its in it's infancy around here.
What I find is that getting lines is a serious problem and most are geared towards Spey casting, even with the overhead system the lines are still like rope. Thats why I like the T40, its thin, heavy, fits a 9# DH rod like a glove and casts like a rocket and sinks like a brick. Personally I hate floating and intermediate lines of any kind. I much prefer fast sinking heads. Max